I got this problem also. I looked around and found an aswer that worked just fine.
The duplicate titles issue happens because you have not uploaded all the latest language files in your Moodle installation. Specifically you need:
- lang/en/block_online_users.php
- lang/en/block_course_summary.php
If you do upload these in your language directory, the duplicate name issue will be resolved.
I got this answer from: Jon Papaioannou